Long-term results of uncemented alumina acetabular implants

We report the clinical and tribological performance of 67 ceramic acetabular prostheses implanted between 1976 and 1979 without bone cement. They articulated with ceramic femoral heads mounted on mental femoral stems. After a mean elapsed period of 144 months, 59 sockets were radiographically stable but two showed early signs and six showed late signs of loosening. Four of the loose sockets have been revised. Histological analysis of the retrieved tissue showed a fibrous membrane around all the implants, with fibrocartilage in some. There was no bone ingrowth, and the fibrous membrane was up to 6 mm thick and infiltrated with lymphocytes, plasma cells, and macrophages. Intra- and extracellular birefringent wear particles were seen. Tribological analysis showed total wear rates in two retrieved alumina-on-alumina joints of 2.6 microns per year in a stable implant and 68 microns in a loose implant. Survival analysis showed a revision rate of 12.4% at 136 months.

Long-term results of uncemented alumina acetabular implants

We report the clinical and tribological performance of 67 ceramic acetabular prostheses implanted between 1976 and 1979 without bone cement. They articulated with ceramic femoral heads mounted on mental femoral stems. After a mean elapsed period of 144 months, 59 sockets were radiographically stable but two showed early signs and six showed late signs of loosening. Four of the loose sockets have been revised. Histological analysis of the retrieved tissue showed a fibrous membrane around all the implants, with fibrocartilage in some. There was no bone ingrowth, and the fibrous membrane was up to 6 mm thick and infiltrated with lymphocytes, plasma cells, and macrophages. Intra- and extracellular birefringent wear particles were seen. Tribological analysis showed total wear rates in two retrieved alumina-on-alumina joints of 2.6 microns per year in a stable implant and 68 microns in a loose implant. Survival analysis showed a revision rate of 12.4% at 136 months.

Cerebellar astrocytoma with extensive lipidization mimicking adipose tissue

We report the case of an elderly woman with a history of headache, vomiting and dizziness while walking. On CT scans a mass was identified in the right cerebellar hemisphere exhibiting radiological characteristics of lipomatous tissue. Surgery revealed a compact lesion consisting of whitish-yellow tissue with a fatty aspect and texture. Smears of tissue samples and paraffin sections showed features suggestive of tissue mainly composed of fully differentiated lipocytes. Lipid-specific stainings on fresh frozen material confirmed univacuolar intracytoplasmic fat accumulation. However, immunohistochemistry for glial fibrillary acidic protein and electron microscopy clearly demonstrated the glial lineage of these lipid-laden cells. Therefore, the tumor was diagnosed as a highly lipidized astrocytoma. In our view, this case represents a variant of lipidized gliomas that has not been described previously and that differs phenotypically from the entities documented earlier.

Perineural tumor extension of facial malignant melanoma: CT and MRI

A case of retrograde perineural tumor that spread from malignant melanoma of the face is reported. Contrast-enhanced CT and plain and contrast-enhanced MR studies, including fat suppression technique, showed tumor extension along the maxillary division of the trigeminal nerve. Histopathological examination of the surgical specimen revealed neurotropic malignant melanoma and confirmed the extent of tumor spread in the perineurium.

Final height after treatment for childhood acute lymphoblastic leukemia: comparison of no cranial irradiation with 1800 and 2400 centigrays of cranial irradiation

We analyzed growth and final heights in 127 patients (68 female patients) treated for childhood acute lymphoblastic leukemia. Central nervous system prophylaxis included either no cranial radiation therapy (CRT) (n = 38), irradiation with 1800 centigrays (cGy) (n = 36), or irradiation with 2400 cGy (n = 53). None of the patients received spinal irradiation. Mean (+/- SEM) age at diagnosis was 6.4 +/- 0.25 years, mean height standard deviation score (SDS) at diagnosis was 0.28 +/- 0.12, and mean age at final height was 18.26 +/- 0.19 years. The change in height SDS between diagnosis and achievement of final height was significant for all treatment groups: -0.49 +/- 0.14, no CRT; -0.65 +/- 0.15, 1800 cGy; and -1.38 +/- 0.16, 2400 cGy. Irradiated patients had a greater loss in height SDS compared with the nonirradiated patients (p < 0.01), and those treated with 2400 cGy CRT had a greater decrease in final height SDS than the patients treated with 1800 cGy (p < 0.01). Both younger age and female sex were significantly associated with a greater decrease in height SDS in the patients treated with CRT; girls < or = 4 years of age at diagnosis had a mean loss in height SDS that was more than twice that observed for others treated with the same dose of CRT. Thus, although modern regimens for acute lymphoblastic leukemia (no CRT or 1800 cGy CRT) appear overall to have only a modest impact on final height, patients, especially girls, treated with 1800 cGy CRT at a young age remain at risk for clinically significant growth failure.

Divalent cation-induced lipid mixing between phosphatidylserine liposomes studied by stopped-flow fluorescence measurements: effects of temperature, comparison of barium and calcium, and perturbation by DPX

To understand the mechanism of membrane fusion, it is important to study the processes that mix the lipids of two apposed membranes. We measured the rates of divalent cation-induced aggregation and lipid mixing of bovine brain phosphatidylserine (BBPS) LUV, using light scattering and a resonance energy transfer assay. The lipid and divalent cation solutions were combined by stopped-flow mixing, which permitted measuring the half-times of aggregation and lipid mixing between pairs of liposomes. The collisional quencher DPX [p-xylene-bis(pyridinium bromide)], used in a liposome contents-mixing assay, lowered the main transition temperature (Tm) of BBPS by about 10 degrees C and decreased the temperature threshold for lipid mixing. Since DPX was inside the liposomes for the latter measurements, this implies that perturbations to the inner monolayer affect the reactivity of the liposome. When palmitoyl-oleoyl-PS (POPS) was substituted for BBPS, little or no lipid mixing occurred. Ca(2+)- and Ba(2+)-induced BBPS aggregation and lipid mixing were compared as a function of temperature and divalent cation concentration. Aggregation rates were nearly insensitive to temperature and correlated with the percent of PS bound to either Ba2+ or Ca2+. Above Tm, lipid-mixing rates increased with the Ba2+ and Ca2+ concentrations and temperature, even above the Tm of the Ba2+/PS complex. Arrhenius plots were linear for both ions. The temperature dependence was greater for Ca(2+)- than Ba(2+)-induced reactions, and the slopes were independent of divalent cation concentration. When equivalent fractions of PS were bound with divalent cation at, and above, 20 degrees C, the lipid-mixing rate was greater with Ca2+ than with Ba2+. The faster rate may reflect greater activation entropies and/or greater attempt frequencies at one or more steps in the Ca(2+)-induced process. We conclude that stopped-flow mixing permits better characterization of initial interaction between liposomes, that small changes in the acyl chain region of the PS bilayer or the inner monolayer can have large effects on lipid-mixing rates, and that the differences between Ba(2+)- and Ca(2+)-induced interactions may be related to qualitative differences in the destabilization step.

Ion channels in single bilayers induced by rat connexin32

The gap junction channel mediates an important form of intercellular communication, but its detailed study is hindered by inaccessibility in situ. We show here that connexin32, the major protein composing junctional channels in rat liver, forms ion channels in single bilayer membranes. The properties of these reconstituted connexin32 channels are characterized and compared with those of gap junction channels. The demonstration that connexin32 forms channels in single membranes has implications for assembly and regulation of junctional channels, and permits detailed study of the gating, permeability and modulation of this channel-forming protein.

Maternity and medicinal plants in Vanuatu. I. The cycle of reproduction

Ethnobotanical data collection to select pharmacologically active species was carried out within a clearly defined therapeutic context: those plants used during the course of a woman's reproductive life. Extensive bibliographical and field data collection and cross-examination of the information thus gathered have provided us with a clearer picture of the effectiveness of these plant species. Various concepts, behaviours and practices relating to menstruation, pregnancy, birth and birth control were examined in detail from an ethnopharmacological point of view. A list of selected species of particular interest is proposed for further study.

On the material and the tribology of alumina-alumina couplings for hip joint prostheses

The yearly sphericity deviation ranged from 0.03 mu to 3.7 mm in 48 retrieved implants with alumina--alumina bearing balls and cups. Excessive amounts of wear are predominantly design dependent or caused by malalignment. But the abrasion phenomena occurring in the cup centers and in the corresponding ball areas are related to unfavorable function zones. The influence of the lubricating gap geometry as studied in laboratory tests shows the form of sphericity deviations to be of decisive importance for wear and friction, if extended over small angles. Then, the contact stresses attributable to the actual effective curvatures of the bearing exceed the resistance to abrasion of the material under boundary lubrication conditions. There are remarkable differences between the early and actual material quality. Based on the state of knowledge of material aspects of wear criteria for the optimization of material and design, promising tolerable wear rates may be achieved.

Active respiratory syncytial virus purified by ion-exchange chromatography: characterization of binding and elution requirements

Two viruses, respiratory syncytial virus (RSV) and vesicular stomatitis virus (VSV) were used to evaluate viral purification by an affinity resin column (Matrex Cellufine Sulfate (MCS); Amicon Division, WR Grace & Co.). Viable RSV was purified significantly from crude cell lysate by a single pass through a column containing the anionic MCS resin. Most cell protein and albumin eluted from the MCS resin with phosphate buffered saline (PBS) but RSV eluted at high ionic strength, i.e., greater than or equal to 0.6 M NaCl. Further purification was possible by sucrose step gradient centrifugation. The RSV prepared by column purification or by column plus sucrose gradient separation was both intact and infective. RSV and pure samples of VSV were used to optimize ionic strength and salts for elution from the MCS column: 0.8 M NaCl removed most of the viral protein. The capacity of the MCS gel for RSV or VSV was found to be about 0.6-0.8 mg viral protein per ml of hydrated resin. Detergent-solubilized viral membrane proteins bound to the MCS resin in 0.145 M NaCl and eluted with higher salt concentrations. Thus, this resin also may be a useful aid for relatively gentle purification of these proteins.

Differential distribution of immunohistochemical markers in the bed nucleus of the stria terminalis in the human brain

A variety of histochemical findings have contributed to a more differentiated architectonical description of the bed nucleus of the stria terminalis (BNST) in the mammalian brain. However, in the human brain investigations of the chemoarchitecture of this nucleus have been rare. Therefore we chose this region in six human autopsy brains in order to map the distribution patterns of 13 immunohistochemical markers for neurotensin (NT), neuropeptide Y (NPY), somatostatin (SOM), enkephalins (ENK), vasoactive intestinal polypeptide (VIP), substance P (SP), neurophysins (NPH), glial fibrillary acid protein, 3-fucosyl-N-acetyl-lactosamine epitope, myelin basic protein (MBP), calbindin (CAB), synaptophysin (SYN) and chromogranin-A (CHR-A). Three chemoarchitectonically distinct areas could be defined. The lateral subdivision of the BNST contained high amounts of NPY and SP-fibre immunoreactivity and was further characterized by the occurrence of neurons labelled for NPY. The central subdivision of the BNST appeared as a histochemically clearly circumscribed compartment with massive fibre immunoreactivity for SOM, ENK, VIP, SYN, CHR-A, CAB as well as SOM, ENK, NT and CAB positive cells but lacked cytosolic or fibre-like immunolabel for NPY and SP. This structure was also ensheathed by myelinated fibres identified by means of MBP immunohistochemistry. The medial subdivision of the BNST showed moderate to high SP and NPY fibre immunoreactivity but lacked immunolabelled neurons and was only scarcely supplied with varicose or punctiform ENK immunoproduct. In the most posterior levels of our sections a cell group labelled for NPH was located lateral to the fornix columns. The lateral subdivision of the BNST (with NPY, SYN) and mainly the central BNST (with SOM, ENK, VIP, SYN and CHR-A) contributed to ventrolateral extensions of dense patchy fibre immunoreactivity throughout the basal forebrain region.

Membrane solubilization with and reconstitution from surfactant solutions: a comparison of phosphatidylserine and phosphatidylcholine interactions with octyl glucoside

Most structural and functional studies of membrane proteins eventually require that the protein be solubilized from its original membrane, isolated and reconstituted into a membrane composed of native or specific phospholipids. The conditions comprising a successful reconstitution protocol often seem both arbitrary and elusive. The solubilization steps as the neutral surfactant octyl glucoside (OG) is added to the negatively charged lipid phosphatidylserine (PS) were followed by several optical techniques. Vesicle leakage, changes in resonance energy transfer between lipid probes and micelle formation were determined as a function of (PS) and temperature. The (OG) needed at these transitions was linear with (PS) so that average compositions and the free (OG) could be calculated for each point. More OG is needed to solubilize at 15 compared to 35 degrees C reflecting the temperature dependence of pure OG solubility. Although similar, the average compositions of the mixed surfactant-lipid structure and their temperature dependence were not identical to similar points determined for egg phosphatidylcholine and OG.

Solubility properties of the alkylmethylglucamide surfactants

The critical micelle concentration (CMC) and the ability to solubilize and form vesicles from phospholipids are important criteria for the selection of a surfactant for reconstitution protocols. The CMC and its temperature dependence were determined for an homologous series of alkylmethylglucamides (MEGA-8, MEGA-9, MEGA-10). Each detergent was added continuously from a concentrated solution to a saline buffer with the environment-sensitive fluorescent probe ANS, held in a thermojacketed cuvette; ANS fluorescence increases at the CMC. The CMCs at 25 degrees C were 51.3, 16.0 and 4.8 mM for MEGA-8, MEGA-9 and MEGA-10. The free energy change for transfer to a micellar environment per -CH2- was -740 cal/mol, similar to other alkyl series. The CMCs decreased slightly with increasing temperature (T = 5-40 degrees C) for MEGA-9 and MEGA-10 while that of MEGA-8 was virtually insensitive to temperature in this range. MEGA-9 solubilization of egg PC in aqueous solutions was determined as a function of [PC] and temperature. The lamellar-micellar phase boundaries were determined by simultaneous 90 degrees light scattering and the resonance energy transfer using the headgroup labeled lipid probes NBD-PE and Rho-PE. The [MEGA-9] at solubilization was linear with [PC]; the MEGA-9 to egg PC ratio in the structures at optical clarity was 2.3 while the monomeric [MEGA-9] was 14.3 mM or slightly lower than the CMC at 25 degrees C. Solubilization of egg PC by MEGA-9 was somewhat more temperature-dependent than the CMC of this detergent. Vesicles formed from MEGA-9 tended to be multilamellar. MEGA-9 is clearly different from octyl glucoside, despite its chemical similarity, in terms of its temperature sensitivity and vesicle forming characteristics.

[Late occlusive thrombosis of mitral prosthesis with sinus rhythm. Report of two surgically treated patients]

Two cases are reported of late occlusive thrombosis of a mitral bioprosthesis with sinus rhythm. Two men were concerned (40 and 54 years of age), hospitalized for acute pulmonary oedema which was resistant to medical treatment, 3 years after replacement of a mitral valve (Carpentier Edwards No. 31 and Liotta No. 25). Catheterization showed that in both cases there was an average transmitral holodiastolic gradient greater than 25 mmHg. Emergency surgery revealed two anatomical forms of occlusive thrombosis: in one case, a localized red thrombus hindered the opening of a valve cusp; in the other, exuberant fibrin deposits lined the ventricular face of the valve cusps. There were no signs of degeneration of the bioprostheses and, in particular, there was no calcification. Both patients were asymptomatic 1.5 years and 3 years respectively after their operations. Late occlusive thromboses of mitral bioprostheses are exceptional (13 detailed cases collected from the literature).

Mapping of neuropeptide Y-like immunoreactivity in the human forebrain

By means of immunohistochemistry the distribution of neuropeptide Y (NPY)-containing neurons and fibres was determined in the human forebrain on the basis of frontal paraffin sections from six individuals of different biological age. NPY was located in abundance in telencephalic cortical and subcortical structures like the striatum, the amygdaloid body and the substantia innominata. Variations in the distribution of immunoreactivity were observed and correlated with distinct subdivisions and structural elements of the basal forebrain region identified by Weigert or Nissl-stained neighbouring sections. The diencephalon was characterized by a relative paucity of labeled cells which were mostly confined to the area of the Nc. infundibularis and the median eminence while fibers were widely distributed in high density in most hypothalamic subnuclei except for the supraoptic nucleus. A periventricular zone of high fibre immunoreactivity was observed in the thalamus. NPY distribution in the developing brain was characterized by the finding of numerous labeled perikarya in the subcortical white matter and by far higher densities of labeled cells in the striatum as compared to the adult brain.

Temperature dependence of the vesicle-micelle transition of egg phosphatidylcholine and octyl glucoside

The temperature dependence of octyl glucoside micellization was determined and compared to the phase behavior of the octyl glucoside--egg phosphatidylcholine (PC) mixed system in excess water to help elucidate the process of vesicle formation from mixed surfactant-phospholipid micelles. The critical micelle concentration of octyl glucoside (OG) was determined from the sharp increase of ANS fluorescence at micellization in an NaCl buffer at temperatures ranging from 5 to 40 degrees C. The cmc decreased with increasing temperature from 31 mM at 5 degrees C to 16 mM at 40 degrees C. A similar but less steep temperature dependence is observed for the solubilization of egg PC vesicles by OG as monitored by the surfactant-dependent changes in (1) solution turbidity and (2) the resonance energy transfer between NBD-PE and Rho-PE incorporated in the vesicles. These assays identify two breakpoints, most likely the boundaries of the cylindrical micelle and spheroidal micelle coexistence region. The [OG]aq values at these two breakpoints have similar temperature dependencies. However, the cylindrical mixed micelles at the boundary have nearly identical OG:PC ratios over the temperature range studied, whereas the spheroidal mixed micelles have relatively more OG at the higher temperatures (OG:PC ratio increases from 2.92 to 3.72 between 5 and 35 degrees C). Estimation of the acyl volume to surface area ratio for the compositions observed suggests that this parameter remains constant over temperature. The spheroidal mixed micelles, but not the cylindrical PC-OG micelles, exhibit ideal mixing between the two components at all temperatures (5-35 degrees C). This temperature sensitivity may be utilized to improve the efficacy of membrane protein reconstitution.(ABSTRACT TRUNCATED AT 250 WORDS)

Vesicle-micelle transition of phosphatidylcholine and octyl glucoside elucidated by cryo-transmission electron microscopy

Vesicle-micelle transition structures of egg phosphatidylcholine (PC) and octyl glucoside (OG) mixtures were observed in the vitrified hydrated state by cryo-transmission electron microscopy (cryo-TEM) and correlated with the macroscopic and molecular changes previously associated with micellization monitored by 90 degrees light scattering and resonance energy transfer between fluorescent lipid probes. Several distinct structural changes occurred as OG was added to the PC vesicles. First, the average vesicle size decreased from 160 nm to less than 66 nm with no apparent change or decrease in optical density (OD). Then, associated with a small rise in OD, samples with open vesicles were observed coexisting with pieces of lamellae and long cylindrical micelles; more micelles were seen at higher [OG]. This mixture of vesicles and cylindrical micelles occurred in the region of the phase diagram previously attributed to vesicle opening, and possibly vesicle size increase. At higher [OG], small spheroidal micelles coexisting with cylindrical micelles correlated with a decrease in OD and changes in the fluorescence signal. At high [OG] when the solution appeared clear, spheroidal micelles were the dominant structure. By using cryo-TEM, a technique which preserves the original microstructure of fluid systems and provides direct images at 1 nm resolution, we have elucidated the vesicle-micelle transition and identified intermediates not known previously in the PC/OG system.

Cerebral phaeohyphomycosis caused by Chaetomium globosum in a renal transplant recipient

A 32-year-old male patient developed headaches, vomiting, blurring of vision, and focal seizures of the left side of the face 2 months after a renal transplant. He developed a brain abscess and died. Direct KOH examination of the brain tissue demonstrated hyaline as well as dematiaceous, septate hyphae. Histologic examination of brain sections revealed polymorphous fungal elements consisting of septate, dark-pigmented hyphae, intercalary and terminal swollen fungal cells, and budding yeastlike cells characteristic of phaeohyphomycosis. Chaetomium globosum was isolated from the brain tissue on all of the fungal media used. This case represents the first histologically and culturally documented phaeohyphomycotic brain infection caused by C. globosum.

Transport-specific isolation of large channels reconstituted into lipid vesicles

To develop a technique for purifying and identifying pore-forming membrane proteins, we used a transport-specific increase in buoyant density to select for lipid vesicles containing voltage-dependent anion channels (VDAC). Monodisperse, single-walled vesicles were formed by gel filtration from a detergent-solubilized mixture of lipid and protein in a urea buffer. The vesicles were layered on a linear iso-osmolar density gradient formed of urea and sucrose buffers. Since VDAC is open at zero trans-membrane voltage and is permeable to urea and sucrose, vesicles containing functional VDAC should become more dense as sucrose enters and urea leaves, while those lacking open channels should maintain their original density. Vesicles formed in the absence of VDAC migrated to a characteristic density, while vesicles formed in the presence of VDAC fractionated into two populations in the gradients, one migrating to the same density as the vesicles formed without VDAC, and one at a significantly greater density. In contrast to the lower density vesicles, the higher density vesicles showed a high permeability to calcein, and contained functional VDAC channels (shown by electrophysiological recordings following fusion with a planar bilayer). Thus, vesicles containing open channels were separable from those that did not by a transport-specific shift in density. This technique may be useful for the enrichment of channels of known permeability properties from impure material.

Structural differences between histone H1 molecules from sea urchin (Strongylocentrotus intermedius) sperm and calf thymus: hydrodynamic and c.d. studies

Comparative sedimentation, diffusion and circular dichroism (c.d.) measurements have been performed on two histones H1 from sperm of the sea urchin Strongylocentrotus intermedius (H1S) and from calf thymus (H1T), at a high salt concentration of M NaCl. Both the Stokes radius and the frictional ratio derived from the hydrodynamic parameters were found to be somewhat smaller for H1S than the corresponding values for H1T. In view of the considerably higher molar mass of H1S compared with that of H1T, this result indicates that H+S in 2 M NaCl has a more compact conformation than H1T, probably due to a higher degree of secondary structure in the flanking domains of H1S. The c.d. measurements likewise show that H1S has a higher content of ordered structures than H1T. Model considerations indicate that the C-terminal tail of H1S is the main candidate for accommodation of these additional secondary structure regions.

Composition of octyl glucoside-phosphatidylcholine mixed micelles

The composition of mixed micelles of egg phosphatidylcholine (PC) and octyl glucoside was studied by a novel technique based on measuring resonance energy-transfer efficiency between two fluorescent lipid probes present in trace amounts. Equations were derived for calculating the stoichiometry of the composition of mixed micelles from the energy-transfer measurements. These were applied to determining the average number of lipid molecules in the octyl glucoside-egg PC mixed micelle as a function of detergent concentration. The average number of detergent molecules in these mixed micelles was independent of lipid concentration in the range studied (0-500 microM). The dependence of mixed micelle stoichiometry on the concentration of aqueous (monomeric) octyl glucoside is consistent with the assumptions of ideal mixing of the two amphiphiles in the mixed micelles and that mixed micelles can be treated as a distinct phase.

Activation of vesicular stomatitis virus fusion with cells by pretreatment at low pH

Fusion of vesicular stomatitis virus (VSV) with Vero cells was measured after exposure of the virus to low pH under a variety of experimental conditions. The method of relief of fluorescence self-quenching of the probe octadecylrhodamine was used to monitor fusion. Incubation of the virus at pH 5.5 prior to binding to cells led to significant enhancement of fusion at the plasma membrane, whereas fusion via the endocytic pathway was inhibited. Fusion of pH 5.5-pretreated VSV showed a similar pH threshold for fusion as nontreated virus, and it was blocked by antibody to VSV G protein. Activation of VSV by pretreatment at low pH was only slightly dependent on temperature. In contrast, when VSV was first bound to target cells and subsequently exposed at 4 degrees C to the low pH, activation of the fusion process did not occur. The pH 5.5-mediated activation of VSV could be reversed by returning the pH to neutral in the absence of target membranes. The low pH pretreatment also led to aggregation of virus; large aggregates could be pelleted by low speed centrifugation and only the effects of the supernatant, which consist of single virions and/or microaggregates, were considered. The data were analyzed in the framework of an allosteric model according to which viral spike glycoproteins undergo a pH-dependent conformational transition to an active (fusion-competent) state. Based on that analysis we conclude that the conformational transition to the active state is rate-limiting for fusion and that the viral spike glycoproteins are fusion-competent only in their protonated form.

Micelle-vesicle transition of egg phosphatidylcholine and octyl glucoside

The dissolution and formation of egg phosphatidylcholine (PC) vesicles by the detergent octyl glucoside were examined systematically by using resonance energy transfer between fluorescent lipid probes, turbidity, and gel filtration chromatography. Resonance energy transfer was exquisitely sensitive to the intermolecular distance when the lipids were in the lamellar phase and to the transitions leading to mixed micelles. Turbidity measurements provided information about the aggregation of lipid and detergent. Several reversible discrete transitions between states of the PC-octyl glucoside system were observed by both methods during dissolution and vesicle formation. These states could be described as a series of equilibrium structures that took the forms of vesicles, open lamellar sheets, and mixed micelles. As detergent was added to an aqueous suspension of vesicles, the octyl glucoside partitioned into the vesicles with a partition coefficient of 63. This was accompanied by leakage of small molecules and vesicle swelling until the mole fraction of detergent in the vesicles was just under 50% (detergent:lipid ratio of 1:1). Near this point, a transition was observed by an increase in turbidity and release of large molecules like inulin, consistent with the opening of vesicles. Both a turbidity maximum and a sharp increase in fluorescence were observed at a detergent to lipid mole ratio of 2.1:1. This was interpreted as the lower boundary of a region where both lamellar sheets and micelles are at equilibrium. At a detergent:lipid ratio of 3.0:1, another sharp change in resonance energy transfer and clarification of the suspension were observed, demarcating the upper boundary of this two-phase region. This latter transition is commonly referred to as solubilization.(ABSTRACT TRUNCATED AT 250 WORDS)

pH-dependent fusion of vesicular stomatitis virus with Vero cells. Measurement by dequenching of octadecyl rhodamine fluorescence

We have studied fusion between membranes of vesicular stomatitis virus (VSV) and Vero cells using an assay for lipid mixing based on the relief of self-quenching of octadecylrhodamine (R18) fluorescence. We could identify the two pathways of fusion by the kinetics of R18 dequenching, effects of inhibitors, temperature dependence, and dependence on osmotic pressure. Fusion at the plasma membrane began immediately after lowering the pH below 6 and showed an approximately exponential time course, whereas fusion via the endocytic pathway (pH 7.4) became apparent after a time delay of about 2 min. Fusion via the endocytic pathway was attenuated by treating cells with metabolic inhibitors and agents that raise the pH of the endocytic vesicle. A 10-fold excess of unlabeled virus arrested R18VSV entry via the endocytic pathway, whereas R18 dequenching below pH 6 (fusion at the plasma membrane) was not affected by the presence of unlabeled virus. The temperature dependence for fusion at pH 7.4 (in the endosome) was much steeper than that for fusion at pH 5.9 (with the plasma membrane). Fusion via the endocytic pathway was attenuated at hypo-osmotic pressures, whereas fusion at the plasma membrane was not affected by this treatment. The pH profile of Vero-VSV fusion at the plasma membrane, as measured by the dequenching method, paralleled that observed for VSV-induced cell-cell fusion. Fusion was blocked by adding neutralizing antibody to the Vero-VSV complexes. Activation of the fusion process by lowering the pH was reversible, in that the rate of fusion was arrested by raising the pH back to 7.4. The observation that pH-dependent fusion occurred at similar rates with fragments and with intact cells indicates that pH, voltage, or osmotic gradients are not required for viral fusion.

Polylysine induces pH-dependent fusion of acidic phospholipid vesicles: a model for polycation-induced fusion

Polylysine induced aggregation and fusion of negatively charged small unilamellar phosphatidylcholine vesicles containing at least 10% anionic lipid. Aggregation was followed by absorbance changes and fusion was assayed both by electron microscopy and by fluorescence energy transfer between lipid probes. A method for preparing asymmetric vesicles, where the fluorescent probes were present only in the inner monolayer of the vesicle membrane, was developed. These vesicles were used to distinguish the inner and outer monolayer when measuring lipid mixing between vesicles. Since polylysine induced lipid mixing of both monolayers equally, fusion of these vesicles did occur. The extent of fusion was dependent on the charge ratio between bound polylysine and phosphatidylserine (PS) in the outer monolayer and was optimal at a ratio of about 1:1. Excess polylysine inhibited fusion. At a given concentration of polypeptide, fusion increased as the pH was lowered toward 3 with an apparent pKa near 4. Since this value is close to the pKa of the PS-carboxyl groups and far from the pKa of the lysine epsilon-amino groups, the pH dependence observed for fusion resides in the lipids rather than in the peptide. Fusion was dependent on the available lysine and not the size or molarity of the polypeptide. The data indicate that there must be sufficient sites on the vesicles and sufficient polypeptide to achieve effective aggregation. For fusion to occur after aggregation, charges on the vesicles must be neutralized either by polypeptide-PS interaction or by protonation of the PS carboxyl groups. Optimal conditions for fusion occur when charge neutralization is possible without completely covering the vesicles with polypeptide. The results are consistent with the notion that the polypeptide is necessary for fusion because of requirements for crosslinking, but limits fusion by steric inhibition.

Permeability of small nonelectrolytes through lipid bilayer membranes

Diffusion of small nonelectrolytes through planar lipid bilayer membranes (egg phosphatidylcholine-decane) was examined by correlating the permeability coefficients of 22 solutes with their partition coefficients between water and four organic solvents. High correlations were observed with hexadecane and olive oil (r = 0.95 and 0.93), but not octanol and ether (r = 0.75 and 0.74). Permeabilities of the seven smallest molecules (mol wt less than 50) (water, hydrofluoric acid, hydrochloric acid, ammonia, methylamine, formic acid and formamide) were 2- to 15-fold higher than the values predicted by the permeabilities of the larger molecules (50 less than mol wt less than 300). The "extra" permeabilities of the seven smallest molecules were not correlated with partition coefficients but were inversely correlated with molecular volumes. The larger solute permeabilities also decreased with increasing molecular volume, but the relationship was neither steep nor significant. The permeability pattern cannot be explained by the molecular volume dependence of partitioning into the bilayer or by the existence of transient aqueous pores. The molecular volume dependence of solute permeability suggests that the membrane barrier behaves more like a polymer than a liquid hydrocarbon. All the data are consistent with the "solubility-diffusion" model, which can explain both the hydrophobicity dependence and the molecular volume dependence of nonelectrolyte permeability.

Sizing and separation of liposomes, biological vesicles, and viruses by high-performance liquid chromatography

The ability of an HPLC gel exclusion column (TSK G6000PW) to separate lipid vesicles, viruses, and biological vesicles according to size was tested and compared with separations on Sephacryl S1000. The columns were calibrated using vesicular Stokes radii determined by quasielastic light scattering. The vesicles separated according to size on both types of column and remained intact during elution. Viruses of known diameters and clathrin-coated vesicles were also eluted as a function of size. The TSK G6000PW column was able to separate larger particles (greater than 500 nm) than the Sephacryl S1000, and, when used in combination with the TSK G5000PW column, gave more discrete separations of smaller particles (10 to 30 nm diameter). Moreover, the HPLC columns can be run significantly faster (10-20 min vs several hours) and give more precise results than Sephacryl S1000. Therefore, HPLC using a G6000PW column alone, or in combination with a G5000PW column, provides a rapid and accurate means of sizing and selecting specifically sized biological and artificial vesicles.

Interaction of anthracycline antibiotics with biopolymers: comparative studies of DNA binding and antimicrobial activity of rhodomycin-type anthracycline antibiotics

The binding of the anthracyclines beta-rhodomycin-I and beta-rhodomycin-II to calf thymus DNA was investigated by both equilibrium and kinetic methods taking into account ligand dimerization (ionic strength I = 0.2 M, pH 6.0). The analysis was based upon a cooperative single-step binding mechanism with overlapping of potential binding sites on a linear homogeneous lattice. Equilibrium binding parameters were estimated from spectrophotometric titration experiments by means of a nonlinear fitting program. The results were compared with those obtained previously for the related antibiotic iremycin and were complemented by kinetic parameters determined from temperature-jump experiments at high binding ratio. The binding constants and the mean attachment times of the drugs were found to increase in the serial order iremycin, beta-rhodomycin-I and beta-rhodomycin-II, which is in line with their increasing antimicrobial activity on Bacillus subtilis ATCC 6633.

Apocytochrome c induces pH-dependent vesicle fusion

The ability of apocytochrome c and the heme containing respiratory chain component, cytochrome c, to induce fusion of phosphatidylcholine (PC) small unilamellar vesicles containing 0-50 mol % negatively charged lipids was examined. Both molecules mediated fusion of phosphatidylserine (PS):PC 1:1 vesicles as measured by energy transfer changes between fluorescent lipid probes in a concentration- and pH-dependent manner, although cytochrome c was less potent and interacted over a more limited pH range than the apocytochrome c. Maximal fusion occurred at pH 3, far below the pKa of the 19 lysine groups contained in the protein (pI = 10.5). A similar pH dependence was observed for vesicles containing 50 mol % cardiolipin (CL), phosphatidylglycerol (PG), and phosphatidylinositol (PI) in PC but the apparent pKa values varied somewhat. In the absence of vesicles, the secondary structure of apocytochrome c was unchanged over this pH range, but in the presence of negatively charged vesicles, the polypeptide underwent a marked conformational change from random coil to alpha-helix. By comparing the pH dependencies of fusion induced by poly-L-lysine and apocytochrome c, we concluded that the pH dependence derived from changes in the net charge on both the vesicles and apocytochrome c. Aggregation could occur under conditions where fusion was imperceptible. Fusion increased with increasing mole ratio of PS. Apocytochrome c did induce some fusion of vesicles composed only of PC with a maximum effect at pH 4. Biosynthesis of cytochrome c involves translocation of apocytochrome c from the cytosol across the outer mitochondrial membrane to the outer mitochondrial space where the heme group is attached. The ability of apocytochrome c to induce fusion of both PS-containing and PC-only vesicles may reflect characteristics of protein/membrane interaction that pertain to its biological translocation.

Monocarboxylic acid permeation through lipid bilayer membranes

The membrane permeability coefficients for the homologous monocarboxylic acids, formic through hexanoic, as well as benzoic and salicylic, were determined for egg phosphatidylcholine-decane planar bilayer membranes. The permeabilities of formic, acetic and propionic acid were also determined for "solvent-free" phosphatidylethanolamine bilayers. Permeability coefficients were calculated from tracer fluxes measured under otherwise symmetrical conditions, and precautions were taken to ensure that the values were not underestimated due to unstirred layer effects. The relation between the nonionic (HA) permeability (Pm) and the hexadecane/water partition coefficient (Kp) was: log Pm = 0.90 log Kp + 0.87 (correlation coefficient = 0.996). Formic acid was excluded from the analysis because its permeability was sixfold higher than predicted by the other acids. The permeabilities for "solvent-free" membranes were similar to those for decane-containing membranes. The exceptionally high permeability of formic acid and the high correlation of the other permeabilities to the hexadecane/water partition coefficient is a pattern that conforms with other nonelectrolyte permeabilities through bilayers. Similarly, the mean incremental free energy change per methylene group (delta delta G/-CH2-) was -764 cal mol-1, similar to other homologous solutes in other membrane systems. However, much less negative delta delta G values (-120 to -400 cal mol-1) were previously reported for fatty acids permeating bilayers and biological membranes. These values are due primarily to unstirred layer effects, metabolism and binding to membranes and other cell components.

[Material-specific wear of ceramic/ceramic sliding surfaces in revised hip endoprostheses--clinical and technological considerations]

After more than 8 years of "in-vivo"-experience with ceramic bearing surfaces in hip endoprostheses clinical and tribological aspects of damage-analysis in 29 cases of retrieved Al2O3 prostheses are performed. The balls and sockets are investigated in view of wear-quantification by relative metric determination and wear-quantification by SCAN-microscopy. In 2/3 of all cases the microstructure average grain standard was superelevated. As hypothesis of the destruction mechanism an avalanche-like acceleration of grain-excavations is discussed.